Metacat

/**

 *  '$RCSfile$'

 *  Copyright: 2009 University of New Mexico and the 

 *                  Regents of the University of California

 *

 *   '$Author: costa $'

 *     '$Date: 2009-07-27 17:47:44 -0400 (Mon, 27 Jul 2009) $'

 * '$Revision: 4999 $'

 *

 * This program is free software; you can redistribute it and/or modify

 * it under the terms of the GNU General Public License as published by

 * the Free Software Foundation; either version 2 of the License, or

 * (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, write to the Free Software

 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

 * 

 * Additional Copyright 2006 OCLC, Online Computer Library Center

 * Licensed under the Apache License, Version 2.0 (the "License");

 * you may not use this file except in compliance with the License.

 * You may obtain a copy of the License at

 *

 * http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package edu.ucsb.nceas.metacat.oaipmh.harvester;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.io.InputStream;

import java.io.StringWriter;

import java.net.HttpURLConnection;

import java.net.URL;

import java.util.Date;

import java.util.HashMap;

import java.util.StringTokenizer;

import java.util.zip.GZIPInputStream;

import java.util.zip.InflaterInputStream;

import java.util.zip.ZipInputStream;

import javax.xml.parsers.DocumentBuilder;

import javax.xml.parsers.DocumentBuilderFactory;

import javax.xml.parsers.ParserConfigurationException;

import javax.xml.transform.OutputKeys;

import javax.xml.transform.Result;

import javax.xml.transform.Source;

import javax.xml.transform.Transformer;

import javax.xml.transform.TransformerException;

import javax.xml.transform.TransformerFactory;

import javax.xml.transform.dom.DOMSource;

import javax.xml.transform.stream.StreamResult;

import org.apache.log4j.Logger;

import org.apache.xpath.XPathAPI;

import org.w3c.dom.DOMImplementation;

import org.w3c.dom.Document;

import org.w3c.dom.Element;

import org.w3c.dom.NodeList;

import org.xml.sax.InputSource;

import org.xml.sax.SAXException;

/**

 * HarvesterVerb is the parent class for each of the OAI verbs.

 * 

 * @author Duane Costa, University of New Mexico, LTER Network Office

 * @author Jeffrey A. Young, OCLC Online Computer Library Center

 */

public abstract class HarvesterVerb {

  /* Class variables */

  private static Logger logger = Logger.getLogger(HarvesterVerb.class);

  public static final String SCHEMA_LOCATION_V2_0 = 

    "http://www.openarchives.org/OAI/2.0/ " +

    "http://www.openarchives.org/OAI/2.0/OAI-PMH.xsd";

  private static HashMap<Thread, DocumentBuilder> builderMap = 

                                         new HashMap<Thread, DocumentBuilder>();

  private static DocumentBuilderFactory documentBuilderFactory = null;

  private static Element namespaceElement = null;

  private static TransformerFactory transformerFactory = 

                                               TransformerFactory.newInstance();

  /* Instance variables */

  private Document document = null;

  private String schemaLocation = null;

  private String requestURL = null;

  /* Constructors */

  /**

   * Mock object creator (for unit testing purposes)

   */

  public HarvesterVerb() {

  }

  /**

   * Performs the OAI request

   * 

   * @param requestURL

   * @throws IOException

   * @throws ParserConfigurationException

   * @throws SAXException

   * @throws TransformerException

   */

  public HarvesterVerb(String requestURL) throws IOException,

      ParserConfigurationException, SAXException, TransformerException {

    this.requestURL = requestURL;

  }

  /* Static initialization code */

  static {

    try {

      /* Load DOM Document */

      documentBuilderFactory = DocumentBuilderFactory.newInstance();

      documentBuilderFactory.setNamespaceAware(true);

      Thread thread = Thread.currentThread();

      DocumentBuilder builder = documentBuilderFactory.newDocumentBuilder();

      builderMap.put(thread, builder);

      DOMImplementation impl = builder.getDOMImplementation();

      Document namespaceHolder = impl.createDocument(

                          "http://www.oclc.org/research/software/oai/harvester",

                          "harvester:namespaceHolder", 

                          null

                                                    );

      namespaceElement = namespaceHolder.getDocumentElement();

      namespaceElement.setAttributeNS(

                          "http://www.w3.org/2000/xmlns/",

                          "xmlns:harvester",

                          "http://www.oclc.org/research/software/oai/harvester"

                                     );

      namespaceElement.setAttributeNS(

                          "http://www.w3.org/2000/xmlns/",

                          "xmlns:xsi", 

                          "http://www.w3.org/2001/XMLSchema-instance"

                                     );

      namespaceElement.setAttributeNS(

                          "http://www.w3.org/2000/xmlns/",

                          "xmlns:oai20", 

                          "http://www.openarchives.org/OAI/2.0/"

                                     );

    } 

    catch (Exception e) {

      e.printStackTrace();

    }

  }

  /* Instance methods */

  /* Primary OAI namespaces */

  /**

   * Get the OAI response as a DOM object

   * 

   * @return the DOM for the OAI response

   */

  public Document getDocument() {

    return document;

  }

  /**

   * Get the OAI errors

   * 

   * @return a NodeList of /oai:OAI-PMH/oai:error elements

   * @throws TransformerException

   */

  public NodeList getErrors() throws TransformerException {

    if (SCHEMA_LOCATION_V2_0.equals(getSchemaLocation())) {

      return getNodeList("/oai20:OAI-PMH/oai20:error");

    } 

    else {

      return null;

    }

  }

  /**

   * Get a NodeList containing the nodes in the response DOM for the specified

   * xpath

   * 

   * @param xpath

   * @return the NodeList for the xpath into the response DOM

   * @throws TransformerException

   */

  public NodeList getNodeList(String xpath) throws TransformerException {

    Document document = getDocument();

    return XPathAPI.selectNodeList(document, xpath, namespaceElement);

  }

  /**

   * Get the OAI request URL for this response

   * 

   * @return the OAI request URL as a String

   */

  public String getRequestURL() {

    return requestURL;

  }

  /**

   * Get the xsi:schemaLocation for the OAI response

   * 

   * @return the xsi:schemaLocation value

   */

  public String getSchemaLocation() {

    return schemaLocation;

  }

  /**

   * Get the String value for the given XPath location in the response DOM

   * 

   * @param xpath

   * @return a String containing the value of the XPath location.

   * @throws TransformerException

   */

  public String getSingleString(String xpath) throws TransformerException {

    Document document = getDocument();

    org.apache.xpath.objects.XObject xobject;

    xobject = XPathAPI.eval(document, xpath, namespaceElement);

    String str = xobject.str();

    return str;

  }

  /**

   * Preforms the OAI request for this OAI-PMH verb

   * 

   * @throws IOException

   * @throws ParserConfigurationException

   * @throws SAXException

   * @throws TransformerException

   */

  public void runVerb() 

          throws IOException, ParserConfigurationException, 

                 SAXException, TransformerException {

    //logger.debug("requestURL=" + requestURL);

    InputStream in = null;

    URL url = new URL(requestURL);

    HttpURLConnection con = null;

    int responseCode = 0;

    do {

      con = (HttpURLConnection) url.openConnection();

      con.setRequestProperty("User-Agent", "OAIHarvester/2.0");

      con.setRequestProperty("Accept-Encoding", "compress, gzip, identify");

      try {

        responseCode = con.getResponseCode();

        //logger.debug("responseCode=" + responseCode);

      } 

      catch (FileNotFoundException e) {

        // assume it's a 503 response

        logger.info(requestURL, e);

        responseCode = HttpURLConnection.HTTP_UNAVAILABLE;

      }

      if (responseCode == HttpURLConnection.HTTP_UNAVAILABLE) {

        long retrySeconds = con.getHeaderFieldInt("Retry-After", -1);

        if (retrySeconds == -1) {

          long now = (new Date()).getTime();

          long retryDate = con.getHeaderFieldDate("Retry-After", now);

          retrySeconds = retryDate - now;

        }

        if (retrySeconds == 0) { // Apparently, it's a bad URL

          throw new FileNotFoundException("Bad URL?");

        }

        System.err.println("Server response: Retry-After=" + retrySeconds);

        if (retrySeconds > 0) {

          try {

            Thread.sleep(retrySeconds * 1000);

          } 

          catch (InterruptedException ex) {

            ex.printStackTrace();

          }

        }

      }

    } while (responseCode == HttpURLConnection.HTTP_UNAVAILABLE);

    String contentEncoding = con.getHeaderField("Content-Encoding");

    //logger.debug("contentEncoding=" + contentEncoding);

    if ("compress".equals(contentEncoding)) {

      ZipInputStream zis = new ZipInputStream(con.getInputStream());

      zis.getNextEntry();

      in = zis;

    } 

    else if ("gzip".equals(contentEncoding)) {

      in = new GZIPInputStream(con.getInputStream());

    } 

    else if ("deflate".equals(contentEncoding)) {

      in = new InflaterInputStream(con.getInputStream());

    } 

    else {

      in = con.getInputStream();

    }

    InputSource data = new InputSource(in);

    Thread t = Thread.currentThread();

    DocumentBuilder builder = builderMap.get(t);

    if (builder == null) {

      builder = documentBuilderFactory.newDocumentBuilder();

      builderMap.put(t, builder);

    }

    document = builder.parse(data);

    String singleString = getSingleString("/*/@xsi:schemaLocation");

    StringTokenizer tokenizer = new StringTokenizer(singleString, " ");

    StringBuffer sb = new StringBuffer();

    while (tokenizer.hasMoreTokens()) {

      if (sb.length() > 0) sb.append(" ");

      sb.append(tokenizer.nextToken());

    }

    String schemaLocationStr = sb.toString();

    this.schemaLocation = schemaLocationStr;

  }

  /**

   * Transform the document content to a string and return it.

   * 

   * @return returnString - the string that results from transforming the

   *                        document

   */

  public String toString() {

    Document document = getDocument();

    Source source = new DOMSource(document);

    StringWriter stringWriter = new StringWriter();

    Result result = new StreamResult(stringWriter);

    try {

      Transformer idTransformer = transformerFactory.newTransformer();

      idTransformer.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "no");

      idTransformer.transform(source, result);

      String returnString = stringWriter.toString();

      return returnString;

    } 

    catch (TransformerException e) {

      return e.getMessage();

    }

  }

}